Process for rolling of threads or threadlike profiles together with apparatus for carrying out the process



Dec. 10, 1968 GROB ET AL 3,415,091

PROCESS FOR ROLLING OF THREADS OR THREADLIKE PROFILES TOGETHER WITH APPARATUS FOR CARRYING OUT THE PROCESS Filed Feb. 7, 1966 5 Sheets-Sheet 1 F p/P/a/P APT W xfi 3 f f? L MR. e

2 f w R /f 02 4 y, oil A I 9" PR/OP ART Dec. 10, 1968 B. GROB ET AL. 3,415,091

PROCESS FOR ROLLING OF THREADS OR THREADLIKE PROFILES TOGETHER WITH APPARATUS FOR CARRYING OUT THE PROCESS Filed Feb. 7. 1966 s Sheets-Sheet 2 S 1 19226? g i Q 02 w l 4 0H IN VEN T ORS BUB/(M414 7 61905 Y HLPMAA A/ JCA/UITZ Dec. 10, 1968 GROB ET AL 3,415,091

PROCESS FOR ROLLING OF THREADS 0R THREADLIKE PROFILES TOGETHER.

WITH APPARATUS FOR CARRYING OUT THE PROCESS Filed Feb. 7, 1966 3 Sheets-Sheet 5 INVENTORJ BUB/(HART 6905 BY #[PMA/IN 6&9'0172 flaw 6W 1% AITQPA/E 4 5 United States Patent 3,415,091 PROCESS FOR ROLLING OF THREADS OR THREADLIKE P R O F I L E S TOGETHER WITH APPARATUS FOR CARRYING OUT THE PROCESS Burkhart Grob, Munich-Solln, and Hermann Schulz,

Munich, Germany, assignors to Ernst Grob Werkzeugund Maschinenfabrik, Munich, Germany Filed Feb. 7, 1966, Ser. No. 525,437 Claims priority, application7(9 ermany, Feb. 9, 1965,

10 Claims. (51. 72-404 ABSTRACT OF THE DISCLOSURE This invention relates to a process and to an apparatus for the rolling of threads or thread-like profiles by profile shaping means working simultaneously on both sides of the workpiece, said profile shaping means comprising rotating form rolls of similar sense and rotating at equal peripheral speeds and which, during their penetration into the workpiece, rotates same around its axis while it moves transversely of its axis in the direction of the smallest spacing between the rolls.

A process for rolling of threads and thread-like profiles by means of form rolls, said process operating as above mentioned, is known as a grooving process. For carrying out said process, thread rolling machines are used in which at least one of the two thread forming rolls is movable transversely of its axis. The workpiece to be threaded is brought between the rolls which are first moved away from each other and held in a first position by means of a suitable holder or support device, said position being ahead of the zone of the smallest spacing-between the rolls and might be called an eccentric position. After feeding of the workpiece into the machine, the rolls are brought toward each other whereby the profile shaping means of the rolls engage the workpiece and rotate same and form a thread on the workpiece.

If the workpiece holder, as is commonly the case, is a lineal member on which the part of the workpiece to be formed is supported on its periphery, the workpiece, because of the enlargement of its outside diameter, rises a little with respect to the support member and moves trans-' versely of its axis in the direction of the smallest space between the rolls. The self-acting transverse axial movement of the workpiece is the reason that the workpiece may not be brought entirely into the area of the smallest space between the rolls because it would then be pushed prematurely through said area during enlargement of its outer diameter and the thread then developed would be incomplete.

The support of the workpiece by a lineal support member when using the grooving process has a further disadvantage, especially for the larger depths of threads or thread-like profiles, in that the movement of the workpiece transverse of its axis caused by the enlargement of its outer diameter can become relatively large and, unless expensive thread rolls of a large diameter are used, a high pressure can occur between the workpiece and the support member because of the offset position of the workpiece. The force resulting from said pressure and the rubbing caused thereby of the rotating workpiece against said support member can easily damage the newly formed threads, especially if the workpiece material is of such nature as to be easily deformed or scuifed.

A further known process comprising positioning the workpiece between points or in pinion blocks, which keep the axis of the workpiece at all times in the same position relative to the thread forming rolls, cannot be used for all workpieces and, furthermore, too much time is wasted in inserting and removing same.

The holding or positioning device must at least partially follow the form roll to keep the workpiece properly spaced between the thread forming rolls. Furthermore, the holding device must allow for the unavoidable axial elolngation of the workpiece. Therefore, holding devices of these kinds are used only in special cases.

To take out or throw out the finished workpiece and to insert a new unworked workpiece, the rolls have to be moved away from each other at the end of the rolling operation.

To prevent the waste of time resulting from movement of the thread rolls toward and away from each other, and the danger of the form rolls striking each other, special thread form rolls with elongated recesses are provided which operate basically according to the grooving process but without the inconvenience of moving the rolls to opened or closed positions. The herein used thread form rolls have profile shaping means beginning at the elongated recesses and constantly increasing in height; the relative position of the thread form rolls remains practically unchanged during the whole process of rolling. However, for the complete forming of the thread, only one peripheral area of the form rolls can be used, which is essentially smaller than the total periphery of the form rolls. The finished workpiece is ejected at the moment when both elongated recesses of the forming rolls meet in the area of the smallest spacing between the rolls, and while the rolls are in these respective angular positions the new workpiece blank is inserted.

The manufacturing of said special thread forming rolls is expensive and the stress they have to take up becomes very high where the material of the workpiece has a high degree of hardness.

So far the thread form rolls have been driven at equal peripheral speeds and therefore in driving they have normally been coupled rigidly to each other.

The purpose of this invention is to eliminate some of the essential disadvantages of the known processes and also to make easier the removal of the finished workpiece by means of a new process for rolling of threads or thread-like profiles which is similar to the grooving process.

The new process for the rolling of threads or threadlike profiles contemplates the use of profile shaping means acting simultaneously on both sides of the workpiece, which are on rolls running in the same direction and at equal peripheral speeds and which during penetration into a workpiece will cause same to rotate about its axis while it moves transversely of its axis in the direction toward the smallest distance between the rolls, said method being characterized in that at least during the movement of the workpiece transversely of its axis the peripheral speed of one thread roll is changed relative to the speed of the other roll so that the workpiece makes a rolling movement both around its own lengthwise axis and also on the thread rolls in the above mentioned direction.

By means of the relative change of the peripheral speeds of the thread rolls, that is, the development of a difference in the peripheral speeds of both rolls, the workpiece can be drawn rotatingly and transversely of its axis into the shaping zone between the form rolls and will appreciably decrease the reaction force acting on the holder or support apparatus. In fact, the workpiece will be lifted somewhat from its support. The workpiece, by means of a difference in the peripheral speed of the form rolls, can be rolled with a controllable speed into the position between the form rolls most favorable for a finish rolling of the thread. The workpiece can be kept in such position during multiple rotations of the form rolls by removing the difference in peripheral speeds of said rolls and it can then, upon again providing a difference in peripheral speed for said rolls, be moved through the zone of smallest spacing between the thread forming rolls to throw the workpiece out beyond said smallest zone.

Basically the process of the invention can be used in known grooving processes, however, the new process can also be used for thread form rolls where relative spaced positions remain unchanged during the whole rolling process.

A suitable apparatus to work out the new process comprises a thread rolling machine having two adjustable thread rolls driven in the same direction and driven at equal peripheral speeds, one of which, at least relative to the other, is movable axiclly against an elastic return force, which machine also has a holder or support apparatus for the workpiece, which is suitable to support the workpiece transversely of its rotatable axis in a position outside the zone of smallest spacing of the rolls while the form rolls act on both sides of the workpiece and which machine is characterized in that both thread forming rolls are coupled through a difference gear which allows them to be driven at different peripheral speeds relative to each other.

The use of a difference gearing makes it possible to increase at a constant rate the difference in the peripheral speeds of the respective thread form rolls from a value of zero and then to decrease same in order to change the rolling in movement of the workpiece between the form rolls in a desired manner. Since at the beginning of insertion of the workpiece between the form rolls, a relatively large force is necessary to push the workpiece into the form rolls, and consequently the holder and support apparatus is used to insert the workpiece, it is advanta geous to conrtol the difference gearing simultaneously with a drive mechanism for the workpiece holder or support apparatus, said workpiece holder or support apparatus being by said mechanism movable in a direction toward the smallest space between the form rolls.

The cooperation of the holder or support apparatus,

however, is necessary only for the insertion of the work piece between the form rolls because the difference in the peripheral speeds of the form rolls is sufficient to move the rotating workpiece to the smallest space between the form rolls. In this case, further movement of the holder or support apparatus can stop while the workpiece is moved between said rolls only by the action on the workpiece caused by the difference in the peripheral speeds of the form rolls.

In order to obtain effective control of the difference gearing and of the drive mechanism for the workpiece support apparatus, control curves, especially cam disks, are preferably provided which for simultaneous control of the gearing and of the drive mechanism are coupled with each other.

The difference gearing for the coupling of both form rolls to each other or with a common drive can be constructed in various ways. For instance, a known planetary or differential gear can be used, one shaft of which is used as a control shaft. An especially simple construction is achieved if one thread form roll is driven by a worm gear which is movable in an axial direction rela tive to the worm wheel, so that the normal rotation of the worm wheel or the thread form roll, coupled with the axial movement of the worm gear imposes an additional angular rotation and, consequently, the rolls will be caused to rotate at different peripheral speeds. During an at rest condition of the worm, the peripheral speeds of both thread form rolls are equal to each other. Each axial movement of the worm from said normal position causes a difference in the peripheral speeds of the thread form rolls corresponding to the speed of such movement and, consequently, causes a rolling movement of the workpiece while it is in engagement under pressure with the two form rolls.

The control of the axial movement of the worm and the control of the movement of the workpiece holder or support apparatus can be effected directly by suitably adjusted levers or control cams or eccentrics, the shape of which makes possible an exact synchronization of these movements.

An especially easy insertion of the workpiece and an easy removal of the rolled workpieces can be achieved according to the invention by arranging the two thread rolls on horizontal axes in a thread rolling machine and by directing the forward movement of the tool holder or support apparatus vertically downwardly.

On such a machine, the workpiece or a series of said workpieces on which work has to be done can be inserted in a horizontal direction in front of the retracted workpiece support apparatus. The workpiece is then urged in the direction of the smallest space between the form rolls by means of a movement of the support member and simultaneously by providing a difference in peripheral speed of the form rolls effecting the rolling of the workpiece. Shortly before the smallest space between the form rolls is reached by the workpiece, the forward urging can be interrupted and the peripheral speed of both form rolls can be made equal so that the Workpiece, as is the case in the end stage of the known grooving rolling, is practically held fixedly between the rolls. When the thread is finished, the workpiece can be moved through the smallest spacing between the thread form rolls by again providing a difference in peripheral speeds of both form rolls and/or also by means of a further forward urging by the support apparatus. The workpiece will now be moved forwardly until it falls down, for instance, into a chute or another apparatus to convey the workpiece to another work station.

With reference to the embodiment shown in the drawing, the inventive process together with apparatus for carrying out same will be illustrated more in detail below.

In the drawings:

FIGURES 1 and la show the beginning step and the final step, respectively, of the known grooving process for threads.

FIGURES 2, 2a and 2b show the steps of the thread rolling process embodying the invention.

FIGURE 3 is a schematical elevation of the arrangement of the thread form rolls, the workpiece support apparatus and the drive mechanism for the thread rolling machine embodying the invention.

FIGURES 1 and 1a illustrate the known grooving thread rolling process for a workpiece W which is sup ported between the thread form rolls 1 and 2 on a sup port member 3. The axis of the workpiece is first positioned a distance s beneath the connecting line 4 between the center points 01 and 02 on the thread form rolls. Both of the rolls have equal peripheral speeds and rotate in the same direction as shown by the arrows 1.

After the workpiece W is inserted, the form roll 2 is moved rightwardly in the direction of the horizontal arrow P (FIGURE 1), whereby the workpiece is clamped between the form rolls and is deformed increasingly or, more particularly, profiled (from the FIGURE 1 cross section to the FIGURE 10 cross section) while same rotates about its axis.

The penetration of the profile shaping means of the form rolls 1 and 2 into the workpiece W results in the material being pushed back to the outer area of the thread paths and increasing the outside diameter of the workpiece W.

As it can be seen in FIGURE 1a, the axis of the workpiece W rises with respect to the support member 3. That is, the workpiece W is moved transversely with respect to its axis in the direction of the smallest space between the form rolls, thereby reducing to the size e the distance of the workpiece axis from the connecting line 4 between the center points of both form rolls. At the same time the pressure angle, which at first was of the value o is also reduced to the smaller value (p.

During said forming of the workpiece W, same is pressed strongly onto the support member 3. Thus, during the last stages of forming, the thread can be easily damaged.

If, according to the invention, the thread form roll 1, for instance, has a little higher peripheral speed than the outer diameter of the form roll 2, the workpiece, because of the difference in peripheral speeds of both of the form rolls, is rolled in the direction toward the smallest space between said form rolls without the aid of the support member. The difference of the peripheral speeds of both of the form rolls can be adjusted appreciably by the self-induced movement of the workpiece W due to the enlargement of its outer diameter. In any case, the pressure force on the workpiece W by the support member 3 is essentially reduced and the danger of damage to the newly produced thread profile is eliminated.

In case the workpiece material is easily deformable, the difference in the peripheral speeds of the form rolls can be kept up longer, even during the time period when the workpiece is in the position shown in FIGURE la, where the forward movement of the form rolls 2 is stopped. In this case, the workpiece W is withdrawn from the support member 3 by means of its rolling in movement between the form rolls and is rolled through the area of the smallest spacing between the form rolls 1 and 2 to the point where the profile shaping means of the form rolls move away from each other so that the workpiece is freed and can be taken out or thrown out automatically from the machine. The removing process is easily achieved if the axes of the form rolls are in a vertical position or if the workpiece is inserted above a pair of horizontally arranged form rolls.

FIGURES 2, 2a and 2b show a use of the invention process in a thread rolling machine whose thread form rolls are not, as is common in the grooving process, moved toward and away from each other but which keep the same spacing at all times. In this case, the workpiece blank W, which at first has a smooth cylindrical surface, is inserted into the machine, preferably from above, be tween the form rolls in the zone of the larger spacing theerbetween, the same being the spacing e from the connecting line 4 between the centerpoints 0 0 of the form rolls. The workpiece is then moved forwardly by a support member 3 toward the zone of the smallest spacing between the form rolls. At the same time, a diiference in the peripheral speeds of both thread form rolls is pro vided to create a suitable rolling movement of the workpiece W between and on the form rolls as same passes through the zone of the smallest spacing between the form rolls.

Of course, the difference in peripheral speeds of the form rolls is chosen in a way that the radial forward movement of the workpiece W is coordinated to the progress of its forming.

. As soon as the axis of the workpiece W comes to the connecting line 4 between the form roll centerpoints, according to FIGURE 20, the forward movement of the support member can be stopped and the difference in peripheral speeds of the form rolls can also be reduced to zero. In this case, the workpiece W stops in its position illustrated in FIGURE 2a until the thread rolling process is completed. A favorable control of the peripheral speeds results in the workpiece moving a little from the support member 3 so that the contact between the tops of the thread profiles and the support arm 3 no longer occurs.

FIGURE 2b shows how, by a renewal of a difference in the peripheral speeds of the form rolls, the workpiece can be rolled through the smallest space between the form rolls to the point, in horizontally arranged thread form rolls, where same falls out downwardly. The workpiece can also, by means of a further forward movement of the support or pressure member, be pushed through the rolls and said support member can then be pulled back for insertion of a new workpiece.

For carrying out the process of the invention described above, a thread rolling machine can be used, which essentially is constructed as a grooving thread rolling machine. The drive of at least one of the thread form roll must be provided with a difference gear which allows the imposition of a faster rotational speed onto said form roll to cause the forward rolling movement: of the workpiece.

One of the thread form rolls must, as is done with thread rolling machines, be movable axially against a restoring force so that said roll, during rotation with higher or smaller peripheral speed, can be adjusted axially in a way that its profile shaping means engage exactly with the thread paths produced on the workpiece by the other roll.

FIGURE 3 illustrates the elements of a suitable thread rolling machine for carrying out the inventive process. The machine is provided, in a known fashion, with two thread form rolls 1 and 2 which are adjustable to the smallest selected space, which rotate about horizontal axes and which have equal outer diameters. One of said thread form rolls is movable relative to the other one against an elastic return force (not shown). The form rolls are driven by drive rolls (also not shown) from a common drive motor each respectively connected to one worm drive 5 or 6, said worm drives 5 or 6 each having a worm wheel 5a or 6a which is respectively connected directly to the form roll 1 or 2 for rotation therewith.

Furthermore, the machine is provided with a vertically guided support or pressure apparatus 3 for the workpiece W which has to be threaded, said apparatus is movable forward and away from the thread of the smallest space between the form rolls by means of an urging and moving mechanism.

The drive mechanism for forward movement of the support or pressure apparatus 3" comprises worm drive 7 which can be driven intermittently and which is provided with a gear 7a which drives two crankings 8 and 9. The crankpin 8 is connected by an elongated connecting rod 10 to a pivot pin 11 at the rearward end of the reciprocably movable support apparatus 3. The crankpin 9 is positioned on a larger radius than the crankpin 8 and is connected flexibly by the connecting rod 12 to one end of a lever 13, which is pivotal about the fixed axis 14 and which is engaged by its other end 15 with the engaging head, the same having a recess 16, of the movable worm guide 17 so that the worm 18 of the worm drive 6 is axially movable. By means of the connecting rod 12, the lever 13 and the worm guide 17, the worm 18 can be moved axially while it drives the worm wheel 6a and the thread form roll 2.

Since both worm drives 5 and 6 have an equal speed changing ratio, normally both thread form rolls 1 and 2 are driven at equal peripheral speeds, During the highest position of both crankpins 8 and 9, the workpiece W is inserted with its axis vertical with respect to the plane of the drawing of FIGURE 3 between the thread form rolls 1 and 2 and the raised support apparatus 3, the same being raised to a suitable stop. Thus, the workpiece, as is shown in FIGURE .2, is at first above the connecting line of the centerpoints of both thread rolls and by means of a slight friction between workpiece and thread roll, the workpiece can be made to rotate. If the wheel 7a is rotated by the worm drive 7 in the direction of the arrow and if both crankpins 8 and 9 are moved into the illustrated position in FIGURE 3, the workpiece support apparatus 3' moves downwardly in the direction of the arrow, while the worm 18 is moved upwardly in the direction of the arrow. The support apparatus 3' presses the workpiece blank W into the narrowing space between rotating thread form rolls 1 and 2 while, by means of a simultaneous moving of the worm 18, an additional angular turning is imposed on the thread form roll 2, which effects a rolling in of the workpiece W on the form rolls and in the direction of the smallest space between the thread form rolls 1 and 2 and results at least in a substantially reduced pressure between the support apparatus 3 and the workpiece W.

The arrangement of the crankpins 8 and 9 and the speed-change ratio of the lever 13 are synchronized with the forward moving of the workpiece W between the thread form rolls 1 and 2, so that the pressure on the side of the workpiece from the support apparatus 3 is relieved as the workpiece W is inserted between the rolls and that simultaneously, by means of the difference in peripheral speeds of both thread form rolls 1 and 2, the workpiece is rolled.

The feeding mechanism illustrated as an example in FIGURE 3 acts as a differential gear for the production of the change in the peripheral speed of one thread form roll relative to the other in the sense of a rolling movement of the workpiece and at the same time acts as a mechanism for forward movement for the support apparatus 3 of the workpiece, whereby by means of the direct mechanical coupling, the desired reciprocal synchronization is achieved.

The synchronization can be varied by means of an angular and radial adjustment of both crankpins 8 and 9 to achieve the most favorable thread rolling conditions.

The adjusting devices which are necessary for this are not shown since they are not new to the man skilled in the art.

The rolling process is accomplished in a manner illustrated in FIGURES 2, 2a and 2b.

If the material of the workpiece W is very hard and if a deeper rolling in a stationary condition with equal peripheral speeds of both thread form rolls 1 and 2 is desired, the mechanism for feeding of the workpiece can be stopped when it reaches the bottom dead center of the crankpins 8 and 9, whereby the workpiece W will be positioned a little above (s the connecting line between both centerpoints of the thread form rolls 1 and 2. The feeding mechanism can also move to the other dead center, or rather through said dead center position, whereby the workpiece W is fed uninterruptedly through the nip between the thread form rolls 1 and 2 by the unequal peripheral speeds of the two thread form rolls.

It should be clear that instead of the mechanism for feeding illustrated in FIGURE 3, other mechanisms can also be used for the production of different peripheral speeds of the thread form rolls and for the mechanical feeding of the workpiece W. The axial movement of the drive worm 18 and of the pressure apparatus 3' can be easily effected by appropriately shaped cams which are driven synchronously or a planetary gearing for driving one thread form roll faster than the second thread roll while at the same time moving forward the support apparatus 3'.

The drive mechanism for achieving a relative rotational speed of thread form rolls and a forward movement of the workpiece support apparatus can be returned by spring forces to re-establish the initial stage or, more particularly, bring back the worm into its normal engaging position.

The thread rolling machine of the invention, for instance, can also be used for profiling surfaces or for roll polishing, if the thread form rolls are exchanged for other suitable rolls.

Although particular preferred embodiments of the invention have been disclosed above in detail for illustrative purposes, it will be recognized that variations or modifications of such disclosure, which come Within the scope of the appended claims, are fully contemplated.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A thread rolling apparatus for forming threads on cylindrical workpieces, comprising:

means for forming threads on a workpiece, said means including a pair of thread form rolls mounted for rotation about substantially parallel axes, said pair of thread form rolls being positioned adjacent one another in spaced relation so as to define a Working gap therebetween, the width of the gap between the peripheries of the rolls being less than the diameter of the cylindrical workpiece;

drive means connected to said pair of thread form rolls for rotating same at substantially equal peripheral speeds;

movable feed means for forcing workpieces into the working gap between the rotating rolls for causing threads to be rolled thereon; and

speed change means operating synchronously with said movable feed means and interconnected to said drive means for causing a relative difference in the peripheral speed of said pair of rolls at the beginning of and during the thread rolling operation for causing the workpiece to roll into the gap, said speed change means further causing said pair of rolls to resume their initial phase and equal peripheral speed relationship after the thread rolling operation has been completed.

2. An apparatus as defined in claim 1, wherein an eccentric driven member is connected to both said movable feed means and said speed change means for synchronous control thereof.

3. An apparatus as defined in claim 1, further including drive means connected to both said movable feed means and said speed change means for synchronously operating same.

4. An apparatus as defined in claim 3, wherein said speed change means is operatively interconnected to one of said rolls for imparting a positive additional peripheral speed thereto relative to said other roll at the beginning of and during the thread rolling operation and, after the thread rolling operation, for imparting a negative additional peripheral speed to the one roll corresponding to the positive additional speed until the initial phase relation between the rolls is restored.

5. An apparatus as defined in claim 3, wherein said feed means includes a reciprocating pressure member which acts laterally on the workpiece for forcing same into the gap.

6. An apparatus as defined in claim 3, wherein said drive means includes a first rotatable worm in driving engagement with a first worm wheel for rotating one of said rolls and a second rotatable worm in driving engagement with a second wheel for rotating said roll, and wherein said speed change means is drivingly connected to said first worm for moving same axially along its rotational axis so as to cause the peripheral speed of said one roll to vary relative to the peripheral speed of said other roll.

7. An apparatus as defined in claim 6, wherein said additional drive means includes a rotatable drive member, and wherein said speed change means includes linkage means drivingly connecting said rotatable drive member to said first rotatable worm for linearly moving same, and wherein said feed means includes a reciprocal pressure member and means drivingly connecting said reciprocal pressure member to said rotatable drive member.

8. An apparatus as defined in claim 7, wherein the linkage means of said speed change means includes a link member in driving engagement with said first rotatable worm at one end thereof and a lever member pivotably mounted to said rotatable member eccentrically thereof, the other end of said link member and said lever member being pivotally connected to each other, and wherein said feed means includes a link pivotally connected at one end thereof to said rotatable drive member in eccentric relationship thereto with the other end of said link being drivingly connected to said reciprocal pressure member.

9. A method for rolling threads on cylindrical workpieces by means of thread form rolls, which rolls rotate in the same direction about substantially parallel axes and are spaced from one another so as to define a gap therebetween, comprising the steps of:

rotating said rolls at substantially equal peripheral speeds; forcing a workpiece laterally into said gap and into contact with said rolls; simultaneously causing a relative difference in the peripheral speed of said rolls for moving said workpiece toward the narrowest portion of said gap; and thereafter restoring said rolls to their initial phase and equal peripheral speed relationship so as to be in condition to have a further workpiece forced into said gap.

10 10. A method as defined in claim 9, wherein the difference in the peripheral speed of said rolls is removed while the workpiece is located at the narrowest portion of said gap.

References Cited UNITED STATES PATENTS 1,107,621 8/1914 Landis 72l04 1,188,461 6/1916 McCain 72l04 2,257,234 9/1941 Gould 72l04 2,355,132 8/1944 Affleck 72l04 2,519,164 8/1950 Watkins et a1. 72104 2,550,855 5/1951 Ostendorf 72l04 2,679,773 6/1954 Scott 72l04 2,932,996 4/1960 Yamamoto 72l04 2,968,201 1/1961 Reed et a1 72l04 3,048,064 8/1962 Hofer 72l04 CHARLES W. LANHAM, Primary Examiner.

E. M. COMBS, Assistant Examiner.

US. Cl. X.R. 

